Hand prostheses that provide one or more electromechanical wearer operable digits are known. Conventional prostheses often use an electric motor mounted in the hand itself and transmit motive power to the digits by means of a transmission system involving mechanical linkages. Such conventional prostheses have a number of shortcomings, notably a requirement for precise alignment between motor and transmission system, which can lead to a cumbersome arrangement, and the imposition of space requirements in the hand portion of the prosthesis, which can make the prosthesis unsuitable for a patient with some residual digits.
WO 95/24875 describes a hand prosthesis that addresses the above noted shortcomings of conventional prostheses. More specifically, the hand prosthesis of WO 95/24875 comprises a drive motor and gearbox mounted within a finger member. Operation of the drive motor drives a worm located within the finger member. The worm engages with and moves around a fixed worm gear wheel to move the finger member about the worm gear wheel axis.
The present inventor has appreciated certain shortcomings of the hand prostheses of WO 95/24875. More specifically, the size of the electromechanical components within the finger member makes it difficult to provide short prosthetic fingers with motors of sufficient power and with gears having appropriate ratios, such as are suitable for children.
It is therefore an aim of the present invention to provide a prosthesis having a digit member configured to provide for a small digit such as is suitable for children.